Resin composition for solar cell encapsulant, solar cell encapsulant and solar cell module using the same

ABSTRACT

A resin composition for a solar cell encapsulant is provided, containing an ethylene•α-olefin copolymer and an organic peroxide or a silane coupling agent or the like, and having superior heat resistance, transparency, flexibility and adhesion property to a glass substrate, as well as good balance between rigidity and cross-linking efficiency, as well as a solar cell encapsulant, and a solar cell module using the same. The resin composition has an ethylene•α-olefin copolymer (A), having the characteristics (a1) to (a4), along with characteristics (a5) or (a6), and an organic peroxide (B) and/or a silane coupling agent (C).

TECHNICAL FIELD

The present invention relates to a resin composition for a solar cell encapsulant, a solar cell encapsulant and a solar cell module using the same, and more specifically the present invention relates to the resin composition for a solar cell encapsulant containing an ethylene•α-olefin copolymer and an organic peroxide or a silane coupling agent or the like, and having superior heat resistance, transparency, flexibility and adhesion property to a glass substrate, as well as good balance between rigidity and cross-linking efficiency, the solar cell encapsulant and the solar cell module using the same.

BACKGROUND ART

In the midst of close-up of a global environmental problem such as increase in carbon dioxide, photovoltaic power generation has been drawn attention again, as well as effective utilization of hydraulic power, wind power, geothermal heat or the like.

The photovoltaic power generation is the one using a packaged solar cell module, obtained in general by protecting a solar cell element of silicon, gallium-arsenic, copper-indium-selenium or the like with an upper transparent protecting material and a lower substrate protecting material, and fixing the solar cell element and the protecting material with an encapsulant made of a resin, and since it can be arranged in a decentralized state at a place where electric power is necessary, although scale thereof is smaller as compared with hydraulic power, wind-power or the like, research and development has been promoted aiming at performance enhancement of power generation efficiency or the like, and price reduction. In addition, by adoption of a policy to subsidize the installment cost, as an introduction promotion business of a residential house photovoltaic power generation system by state or local governments, prevalence thereof has gradually been progressing. However, still more cost reduction is required for further prevalence thereof, and effort has, accordingly, been continued in a step-by-step fashion not only to develop a solar cell element using a novel material instead of conventional-type silicon or gallium-arsenic, but also to further reduce production cost of the solar cell module.

As requisite of the solar cell encapsulant composing the solar cell module, good transparency has been required, so as not to decrease power generation efficiency of the solar cell, and to secure incidence amount of sunlight. In addition, the solar cell module is usually installed outdoors, which raises temperature caused by exposure to sunlight for a long period of time. To avoid such a trouble as deformation of the module by flowing of the encapsulant made of a resin, caused by increase in temperature, it should be the one having heat resistance. In addition, thinning trend has been progressing year by year, to reduce material cost of the solar cell element.

At present, as the encapsulant of the solar cell element in the solar cell module, in view of flexibility, transparency or the like, an ethylene vinyl acetate copolymer, having high content of vinyl acetate, has been adopted as a resin component, where an organic peroxide is used in combination, as a cross-linking agent (for example, see PATENT LITERATURE 1).

And, in an encapsulation work of the solar cell element, the solar cell element is covered with an encapsulant made of a resin, then it is heated for several minutes to ten and several minutes for tentative adhesion, and is heat-treated at high temperature, where the organic peroxide decomposes in an oven, for several minutes to 1 hour for adhesion (for example, see PATENT LITERATURE 2).

However, to suppress production cost of the solar cell module, it has been required to further shorten time required in the encapsulation work, and a solar cell encapsulant has been proposed, which is composed of an α-olefin copolymer which is amorphous or low crystalline with a crystallinity of 40% or less, instead of the ethylene vinyl acetate copolymer, as a resin component of the encapsulant (see PATENT LITERATURE 3). In this PATENT LITERATURE 3, there has been exemplified production of a sheet at a processing temperature of 100° C., using a profile extruder, by mixing an organic peroxide to an amorphous or low crystalline ethylene butene copolymer, however, because of low processing temperature, sufficient productivity has not been obtained.

There was also the case in the solar cell module, where the module may deform, by temperature increase caused by exposure to sunlight for a long period of time, due to installment outdoors as above-described, followed by resultant decrease in adhesion strength between a glass substrate and the encapsulant made of a resin, separation of the encapsulant made of a resin from the glass substrate, and intrusion of air or moisture into space there between. The PATENT LITERATURE 1 has described to blend a silane coupling agent to an encapsulating resin, however, it relates to the solar cell module using a flexible substrate such as a fluorocarbon resin film, and has not clarified detail of the silane coupling agent. The above PATENT LITERATURE 2 has also described to blend a silane coupling agent to the encapsulating resin, however, it relates to the solar cell module using an EVA film and an FRP substrate, and adhesion property with the substrate is not sufficient.

In addition, as the encapsulant of the solar cell module, there has been proposed a polymer material containing an polyolefin copolymer which satisfies one or more requisites among (a) a density of less than about 0.90 g/cc, (b) a 2% secant modulus of less than about 150 megapascal (mPa), measured in accordance with ASTM D-882-02, (c) a melting point of lower than about 95° C., (d) an α-olefin content of at least about 15% by weight and lower than about 50% by weight, based on weight of a polymer, (e) a Tg of lower than about −35° C. and (f) an SCBDI of at least about 50 (see PATENT LITERATURE 3).

In the solar cell module, there is tendency for also the solar cell encapsulant to become thinner accompanying with thinning of the solar cell element. In this case, it has been a problem of easy break of a wiring caused when impact is applied thereto from the upper protecting material side or the lower protecting material side of the solar cell encapsulant. Use of the polymer material of the PATENT LITERATURE 4 is capable of increasing rigidity of the encapsulant, however, it deteriorates cross-linking efficiency, and was thus not practical.

As just described, conventional technology has not provide the resin composition for a solar cell encapsulant with superior productivity, heat resistance, transparency, flexibility and adhesive property to the glass substrate, along with good balance between rigidity and cross-linking efficiency.

CITATION LIST Patent Literature

-   PATENT LITERATURE 1: JP-A-9-116182 -   PATENT LITERATURE 2: JP-A-2003-204073 -   PATENT LITERATURE 3: JP-A-2006-210906 -   PATENT LITERATURE 4: JP-A-2010-504647

SUMMARY OF INVENTION Technical Problem Solution to Problem

It is an object of the present invention to provide the resin composition for a solar cell encapsulant containing an ethylene•α-olefin copolymer and an organic peroxide or a silane coupling agent or the like, and having superior heat resistance, transparency, flexibility and adhesion property to a glass substrate, as well as good balance between rigidity and cross-linking efficiency, the solar cell encapsulant and the solar cell module using the same.

The present inventors have intensively studied a way to solve the above-described problems and obtained the knowledge that the resin composition for a solar cell encapsulant, having superior heat resistance, transparency, flexibility and adhesion property to a glass substrate, as well as good balance between rigidity and cross-linking efficiency, can be obtained by selecting the ethylene•α-olefin copolymer, which was polymerized using a metallocene catalyst as a resin component, and has specified density, molecular weight distribution and melt viscosity characteristics, and blending an organic peroxide or a silane coupling agent thereto, and by using this, productivity of the solar cell module can be enhanced significantly, and have thus completed the present invention.

That is, according to the first aspect of the present invention, there is provided a resin composition for a solar cell encapsulant characterized by comprising the following component (A) and component (B) and/or component (C).

A component A; an ethylene•α-olefin copolymer having characteristics of the following (a1) to (a5)

-   (a1) a density of 0.860 to 0.920 g/cm³ -   (a2) a ratio, (Mz/Mn), of Z average molecular weight (Mz) and number     average molecular weight (Mn) determined by a gel permeation     chromatography (GPC), of 8.0 or less -   (a3) a melt viscosity (η*₁) measured at 100° C. under a shear rate     of 2.43×10 s⁻¹ of 9.0×10⁴ poise or less -   (a4) a melt viscosity (η*₂) measured at 100° C. under a shear rate     of 2.43×10² s⁻¹ of 1.8×10⁴ poise or less -   (a5) a branch number (N) derived from a comonomer in a polymer     satisfying the following expression (a):     N≧−0.67×E+53   expression (a):     (wherein N represents branch number per total 1000 carbon atoms in a     main chain and a side chain, measured by NMR, and E represents     Tensile Modulus of a sheet, measured in accordance with     ISO1184-1983)

A component B; an organic peroxide

A component C; a silane coupling agent

In addition, according to the second aspect of the present invention, there is provided the resin composition for a solar cell encapsulant in the first aspect, characterized in that (a5) the branch number (N) derived from a comonomer in a polymer satisfies the following expression (a′). −0.67×E+80≧N≧−0.67×E+53   expression (a′): (wherein N represents branch number per total 1000 carbon atoms in a main chain and a side chain, measured by NMR; and E represents Tensile Modulus of a sheet, measured in accordance with ISO1184-1983).

In addition, according to the third aspect of the present invention, there is provided a resin composition for a solar cell encapsulant characterized by comprising the following component (A) and component (B) and/or component (C).

A component A; an ethylene•α-olefin copolymer having characteristics of the following (a1) to (a4) and (6):

-   (a1) a density of 0.860 to 0.920 g/cm³ -   (a2) a ratio, (Mz/Mn), of Z average molecular weight (Mz) and number     average molecular weight (Mn) determined by a gel permeation     chromatography (GPC), of 8.0 or less -   (a3) a melt viscosity (η*₁) measured at 100° C. under a shear rate     of 2.43×10 s⁻¹ of 9.0×10⁴ poise or less -   (a4) a melt viscosity (η*₂) measured at 100° C. under a shear rate     of 2.43×10² s⁻¹ of 1.8×10⁴ poise or less -   (a6) a flow ratio (FR): a ratio (I₁₀/I_(2.16)) of I₁₀ which is an     MFR measured value at 190° C. under a load of 10 kg, and I_(2.16)     which is an MFR measured value at 190° C. under a load of 2.16 kg,     of below 7.0

A component B; an organic peroxide

A component C; a silane coupling agent

In addition, according to the fourth aspect of the present invention, there is provided the resin composition for a solar cell encapsulant in the third aspect, characterized in that the flow ratio (FR) of characteristics (a6) is 5.0 to 6.2.

In addition, according to the fifth aspect of the present invention, there is provided the resin composition for a solar cell encapsulant in any of the first to the fourth aspects, characterized in that the content of the component (B) is 0.2 to 5 parts by weight, relative to 100 parts by weight of the component (A).

In addition, according to the sixth aspect of the present invention, there is provided the resin composition for a solar cell encapsulant in any of the first to the fifth aspects, characterized in that the content of the component (C) is 0.01 to 5 parts by weight, relative to 100 parts by weight of the component (A).

In addition, according to the seventh aspect of the present invention, there is provided the resin composition for a solar cell encapsulant in any of the first to the sixth aspects, characterized by further comprising the following component (D).

A component (D): a hindered amine-type light stabilizer.

In addition, according to the eighth aspect of the present invention, there is provided the resin composition for a solar cell encapsulant in the seventh aspect, characterized in that the content of the component (D) is 0.01 to 2.5 parts by weight, relative to 100 parts by weight of the component (A).

In addition, according to the ninth aspect of the present invention, there is provided the resin composition for a solar cell encapsulant in any of the first to the eighth aspects, characterized in that the component (A) is an ethylene•1-butene copolymer or an ethylene•1-hexene copolymer.

Still more, according to the tenth aspect of the present invention, there is provided the resin composition for a solar cell encapsulant in any of the first to the ninth aspects, characterized in that the ethylene•α-olefin copolymer, as the component (A), has the ratio (η*₁/η*₂) of melt viscosity (η*₁) and melt viscosity (η*₂), of 4.5 or less.

On the other hand, according to the eleventh aspect of the present invention, there is provided a solar cell encapsulant obtained by pelletizing or sheeting the resin composition for a solar cell encapsulant in any of the first to the tenth aspects.

Still more, according to the twelfth aspect of the present invention, there is provided a solar cell module using the solar cell encapsulant in the eleventh aspect.

Advantageous Effects of Invention

Because the resin composition for a solar cell encapsulant of the present invention has the ethylene•α-olefin copolymer having specified density, molecular weight distribution and melt viscosity characteristics, as a main component, blending of a silane coupling agent thereto provides good adhesion property to a glass substrate, and also blending of an organic peroxide provides, in sheeting this resin composition, the ethylene•α-olefin copolymer sufficient adhesive strength by cross-linking in a relatively short period of time and good balance between rigidity and cross-linking efficiency, easy formation of a module as the solar cell encapsulant, and is capable of reducing production cost. In addition, the resultant solar cell module is superior in transparency, flexibility, weather resistance or the like, and is expected to maintain stable conversion efficiency for a long period of time.

DESCRIPTION OF EMBODIMENTS

1. The Resin Composition for a Solar Cell Encapsulant

The resin composition for a solar cell encapsulant (hereinafter may be referred to simply as a resin composition) of the present invention is characterized by containing the following ethylene•α-olefin copolymer (A) and the organic peroxide (B) and/or a silane coupling agent (C).

(1) The Component (A)

The component (A) to be used in the present invention is the ethylene•α-olefin copolymer having characteristics of the following (a1) to (a4), and still more preferably the ethylene•α-olefin copolymer having characteristics of (a5) and/or (a6).

-   (a1) a density of 0.860 to 0.920 g/cm³ -   (a2) a ratio, (Mz/Mn), of Z average molecular weight (Mz) and number     average molecular weight (Mn) determined by a gel permeation     chromatography (GPC), of 8.0 or less -   (a3) a melt viscosity (η*₁) measured at 100° C. under a shear rate     of 2.43×10 s⁻¹ of 9.0×10⁴ poise or less -   (a4) a melt viscosity (η*₂) measured at 100° C. under a shear rate     of 2.43×10² s⁻¹ of 1.8×10⁴ poise or less. -   (a5) a branch number (N) derived from a comonomer in a polymer     satisfies the following expression (a).     N≧−0.67×E+53   expression (a):     (wherein N represents branch number per total 1000 carbon atoms in a     main chain and a side chain, measured by NMR, and E represents     Tensile Modulus of a sheet, measured in accordance with     ISO1184-1983) -   (a6) a flow ratio (FR): a ratio (I₁₀/I_(2.16)) of I₁₀ which is an     MFR measured value at 190° C. under a load of 10 kg, and I_(2.16)     which is an MFR measured value at 190° C. under a load of 2.16 kg,     of below 7.0.     (i) Monomer Composition of the Component (A)

The ethylene•α-olefin copolymer to be used in the present invention is a random copolymer of ethylene and an α-olefin, where a composition unit derived from ethylene is a main component.

The α-olefin to be used as the comonomer is the α-olefin having carbon atoms of preferably 3 to 12. Specifically, it includes propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-heptene, 4-methyl-pentene-1,4-methyl-hexene-1, 4,4-dimethyl-pentene-1 or the like. A specific example of such an ethylene•α-olefin copolymer includes an ethylene propylene copolymer, an ethylene•1-butene copolymer, an ethylene•1-hexene copolymer, an ethylene•1-octene copolymer, an ethylene•4-methyl-pentene-1 copolymer or the like. Among these, the ethylene•1-butene copolymer and the ethylene•1-hexene copolymer are preferable. In addition, the α-olefin may be one kind or two or more kinds in combination. In the case of a terpolymer obtained by combining two kinds of α-olefins, it includes an ethylene•propylene•1-hexene terpolymer, an ethylene•1-butene•1-hexene terpolymer, an ethylene•propylene•1-octene terpolymer, an ethylene•1-butene•1-octene terpolymer or the like.

Content of the α-olefin of the ethylene•α-olefin copolymer to be used in the present invention is 5 to 40% by weight, preferably 10 to 35% by weight, and more preferably 15 to 30% by weight. The content within this range provides good flexibility and heat resistance.

The content of the α-olefin here is a value measured by a 13C-NMR method under the following conditions:

Apparatus: JEOL-GSX270, manufactured by JOEL Ltd.

-   Concentration: 300 mg/2 mL -   Solvent: Ortho-dichlorobenzene     (ii) A Polymerization Catalyst and a Polymerization Method for the     Component (A)

The ethylene•α-olefin copolymer to be used in the present invention can be produced using a Ziegler catalyst, a vanadium catalyst or a metallocene catalyst or the like, preferably the vanadium catalyst or the metallocene catalyst, and more preferably the metallocene catalyst. A production method includes a high pressure ionic polymerization method, a vapor-phase method, a solution method, a slurry method, or the like.

The metallocene catalyst is not especially limited, however, such a catalyst is included that a metallocene compound such as a zirconium compound coordinated with a group or the like having a cyclopentadienyl skeleton, and a promoter are used as catalyst components. Commercial products include HARMOREX (registered trademark) series and Kernel (registered trademark) series, produced by Japan Polyethylene Corp.; Evolue (registered trademark) series, produced by Prime Polymer Co., Ltd; Excellen (registered trademark) GMH series, and Excellen (registered trademark) FX series, produced by Sumitomo Chemical Co., Ltd. As the vanadium catalyst, a catalyst having a soluble vanadium compound and an organoaluminum halide as catalyst components are included.

(iii) Characteristics of the Component (A)

(a1) Density

The ethylene•α-olefin copolymer to be used in the present invention has a density of preferably 0.860 to 0.920 g/cm³, more preferably 0.870 to 0.915 g/cm³, and still more preferably 0.875 to 0.910 g/cm³. The density of the ethylene•α-olefin copolymer below 0.860 g/cm³ results in blocking of a sheet after processing, while the density over 0.920 g/cm³ provides too high rigidity of the sheet after processing, giving difficult handling.

In order to adjust polymer density, a method is taken for adjusting, as appropriate, for example, content of the α-olefin, polymerization temperature, catalyst amount or the like. It should be noted that the density of the ethylene•α-olefin copolymer is measured in accordance with JIS-K6922-2: 1997 attachment (the case of a low density polyethylene) (23° C.)

(a2) Ratio (Mz/Mn) of Z Average Molecular Weight (Mz) and Number Average Molecular Weight (Mn).

The ethylene•α-olefin copolymer to be used in the present invention has the ratio (Mz/Mn) of Z average molecular weight (Mz) and number average molecular weight (Mn), determined by a gel permeation chromatography (GPC), of 8.0 or less, preferably 5.0 or less, and more preferably 4.0 or less. In addition, Mz/Mn is 2.0 or more, preferably 2.5 or more, and more preferably 3.0 or more. However, the Mz/Mn over 8.0 deteriorates transparency. Adjusting of Mz/Mn within a predetermined range may be performed by a method for selecting a suitable catalyst system or the like.

It should be noted that measurement of Mz/Mn is performed by the gel permeation chromatography (GPC) under the following conditions:

Apparatus: GPC 150C model, manufactured by Waters Co., Ltd.

Detector: 1A infrared spectrophotometer (a measurement wavelength of 3.42 μm), manufactured by MIRAN Co., Ltd.

Column: Three sets of AD806M/S, manufactured by Showa Denko K.K. (Calibration of the column was performed by measurement of single dispersion polystyrene, produced by Tosoh Corp. (a 0.5 mg/ml solution of each of A500, A2500, F1, F2, F4, F10, F20, F40, and F288), and approximated logarithmic values of eluted volume and molecular weight with a quadratic expression. In addition, molecular weight of the sample was converted to that of polyethylene using viscosity equation of polystyrene and polyethylene•Here, coefficients of the viscosity equation of polystyrene are α=0.723 and log K=−3.967, while those for polyethylene are α=0.733 and log K=−3.407.)

Measurement temperature: 140° C.

Concentration: 20 mg/10 mL

Injection volume: 0.2 mL

Solvent: Ortho-dichlorobenzene

Flow rate: 1.0 ml/minute

It should be noted that because the Z average molecular weight (Mz) has large contribution to average molecular weight of a high molecular weight component, Mz/Mn provides easy confirmation of presence of the high molecular weight component, as compared with Mw/Mn. The high molecular weight component is a factor influencing on transparency, and increase in the high molecular weight component, consequently, deteriorates transparency. In addition, tendency of deterioration of cross-linking efficiency is also observed. Smaller Mz/Mn, therefore, is preferable.

(a3), (a4) Melt Viscosity

The ethylene•α-olefin copolymer to be used in the present invention should have shear rate, measured at 100° C., in a specified range. Reason for focusing on shear rate measured at 100° C. is because of estimating influence on a product in converting a composition at the relevant temperature to the product.

That is, the melt viscosity (η*₁), under the shear rate of 2.43×10 sec⁻¹, is 9.0×10⁴ poise or less, preferably 8.0×10⁴ poise or less, more preferably 7.0×10⁴ poise or less, further preferably 5. 5×10⁴ poise or less, further more preferably 5.0×10⁴ poise or less, particularly preferably 3.0×10⁴ poise or less, and most preferably 2. 5×10⁴ poise or less. It is preferable that the melt viscosity (η*₁) is 1.0×10⁴ poise or more and still more 1.5×10⁴ poise or more. The melt viscosity (η*₁) within this range provides good productivity in low speed molding at low temperature, and generates no problems in processing to a product.

The melt viscosity (η*₁) is adjustable by melt flow rate (MFR) or molecular weight distribution of the ethylene•α-olefin copolymer. Increase in the melt flow rate value tends to decrease the melt viscosity (η*₁). When other property such as molecular weight distribution is different, magnitude relation may be reversed, however, by setting MFR (JIS-K6922-2: 1997 attachment (at 190° C., under a load of 21.18 N)) at preferably 5 to 50 g/10 minutes, more preferably 10 to 40 g/10 minutes, and still more preferably 15 to 35 g/10 minutes, the melt viscosity (η*₁) tends to be easily adjusted within a predetermined range.

Still more, the ethylene•α-olefin copolymer to be used in the present invention should have the melt viscosity (η*₂) measured at 100° C., under the shear rate of 2.43×10² sec⁻¹, is 1.8×10⁴ poise or less, preferably 1.7×10⁴ poise or less, more preferably 1.5×10⁴ poise or less, still more preferably 1.4×10⁴ poise or less, and most preferably 1.3×10⁴ poise or less. It is preferable that the melt viscosity (η*₂) is 5.0×10³ poise or more and still more 8.0×10³ poise or more. The melt viscosity (η*₂) within this range provides good productivity in low speed molding at low temperature, and generates no problems in processing to a product.

Here, the melt viscosity (η*₁), (η*₂) is a measured value obtained by using a capillary rheometer having a capillary with a diameter of 1.0 mm, and L/D=10.

Reason for setting two kinds of shear rates is to obtain a similar product in each of the molding speed regions, with small influence on the product surface in low speed and high speed molding.

In addition, the ethylene•α-olefin copolymer to be used in the present invention has a ratio of η*₁ and η*₂, (η*₁/η*₂), of preferably 4.5 or less, more preferably 4.2 or less, further preferably 4.0 or less, and further more preferably 3.0 or less. The ratio of η*₁ and η*₂, (η*₁/η*₂) is preferably 1.1 or more, and still more preferably 1.5 or more. The (η*₁/η*₂) within the above range provides small influence on the sheet surface, in low speed molding and in high speed molding, and is thus preferable.

(a5) Branch Number (N) Derived from a Comonomer in a Polymer

In the ethylene•α-olefin copolymer to be used in the present invention, it is preferable that the branch number (N) and the tension elastic modulus (E) satisfy the following expression (a): N≧0.67×E+53   Expression (a): (wherein N represents branch number per total 1000 carbon atoms in a main chain and a side chain, measured by NMR, and E represents Tensile Modulus of a sheet, measured in accordance with IS01184-1983).

In the present description, the branch number (N) derived from a comonomer in a polymer can be calculated from a C-NMR spectrum, with reference to, for example, E. W. Hansen, R. Blom, and O. M. Bade, Polymer, Vol. 36, p. 4295 (1997).

In the solar cell module, there is tendency of making a thinner film of the solar cell encapsulant as well, accompanying with making thinner film of the solar cell element. In the solar cell encapsulant made as the thinner film, because of easy break of a wiring when impact is applied thereto from the upper protecting material side or the lower protecting material side, it is required to increase a rigidity of the encapsulant. Increase in the rigidity deteriorates cross-linking efficiency, therefore, it is necessary to use as a material with enhanced moldability, by using a copolymer with a certain high branch degree of a high polymer chain and thus enhancing fluidity of the copolymer before cross-linking. In the present invention, since the branch number (N) derived from the comonomer of the ethylene•α-olefin copolymer has a polymer structure satisfying the expression (a), balance between rigidity and cross-linking efficiency is good.

The ethylene•α-olefin copolymer relevant to the present invention can be produced by a copolymerization reaction using a catalyst, as described above, however, by selecting composition ratio of raw material monomers to be copolymerized, or kind of the catalyst, branch degree in the high polymer chain can easily be adjusted. For the ethylene•α-olefin copolymer to be used in the present invention to satisfy the expression (a), the comonomer in the ethylene•α-olefin copolymer is preferably selected from propylene, 1-butene or 1-hexene•In addition, it is preferable to produce it using a vapor phase method and a high pressure method, and in particular, it is more preferable to select the high pressure method.

More specifically, increasing or decreasing N by fixing E can be attained by a method for changing mainly number of carbon atoms of a comonomer to be copolymerized with ethylene•It is preferable to produce the ethylene•α-olefin copolymer by mixing 1-butene or 1-hexene so as to become an amount of 60 to 80% by weight, relative to ethylene, using a metallocene catalyst, and reacting them at a polymerization temperature of 130 to 200° C. In this way, the branch number N of the ethylene•α-olefin copolymer can be adjusted suitably, and the ethylene•α-olefin copolymer can be obtained, which has a Tensile Modulus E of the resultant sheet of 40 MPa or less, and within a range shown by the expression (a).

In the present invention, a relational expression of characteristics (a5) is preferably shown by the following expression (a′). In addition, a relational expression of characteristics (a5) is preferably shown by the following expression (a″). −0.67×E+80≧N≧−0.67×E+53   Expression (a′): −0.67×E+75≧N≧−0.67×E+54   Expression (a″): (a6) Flow Ratio (FR)

The ethylene•α-olefin copolymer to be used in the present invention preferably has the flow ratio (FR), that is, the ratio (I₁₀/I_(2.16)) of I₁₀ which is an MFR measured value at 190° C. under a load of 10 kg, and I_(2.16) which is an MFR measured value at 190° C. under a load of 2.16 kg, of below 7.0. It should be noted that melt flow ratio (MFR) is a value measured in accordance with JIS-K7210-1999.

It has been known that FR has close relationship with molecular weight distribution and amount of a long chain branch of the ethylene•α-olefin copolymer. In the present invention, among polymers satisfying the above requisites (a1) to (a4), such one is used that has the ratio (I_(10/I) _(2.16)) of an MFR measured value (I₁₀) at 190° C. under a load of 10 kg, and an MFR measured value (I_(2.16)) at 190° C. under a load of 2.16 kg of below 7.0. Use of a copolymer having a polymer structure characterized in such a long chain branch provides good balance rigidity and cross-linking efficiency. On the other hand, the FR of 7.0 or more tends to deteriorate cross-linking efficiency in cross-linking as the solar cell encapsulant.

The FR of the ethylene•α-olefin copolymer to be used in the present invention is below 7.0, preferably below 6.5, and more preferably below 6.3. It should be noted that FR below 5.0 has difficulty in obtaining sufficient rigidity as the solar cell encapsulant. The flow ratio (FR) of characteristics (a6) is most preferably 5.0 to 6.2

(2) The Component (B)

The organic peroxide of the component (B) in the present invention is used to cross-link mainly the component (A).

As the organic peroxide, the organic peroxide having a decomposition temperature (temperature where half-life period is 1 hour) of 70 to 180° C., in particular, 90 to 160° C. may be used. As such organic peroxide, there is included, for example, t-butylperoxy isopropyl carbonate, t-butylperoxy-2-ethylhexyl carbonate, t-butyl peroxyacetate, t-butyl peroxybenzoate, dicumyl peroxide, 2,5-dimethy-2,5-di(t-butylperoxy)hexane, di-t-butyl peroxide, 2,5-dimethy-2,5-di(t-butylperoxy)hexyne-3, 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(t-butylperoxy)cyclohexane, methyl ethyl ketone peroxide, 2,5-dimethyhexyl-2,5-diperoxybenzoate, t-butyl hydroperoxide, p-menthane hydroperoxide, benzoyl peroxide, p-chlorbenzoyl peroxide, t-butyl peroxyisobutyrate, hydroxyheptyl peroxide, cyclohexanone peroxide.

(3) A Blending Ratio of the Component (B)

The blending ratio of the component (B) is preferably 0.2 to 5 parts by weight, more preferably 0.5 to 3 parts by weight, and still more preferably 1 to 2 parts by weight, based on 100 parts by weight of the component (A). The blending ratio of the component (B) lower than the above range does not provide cross-linking or takes longer time in cross-linking. In addition, the ratio higher than the above range provides insufficient dispersion and tends to provide a non-uniform cross-linking degree.

(4) The Component (C)

The component (C) to be used in the resin composition of the present invention is a silane coupling agent, and is used mainly to enhance adhesive strength between the resin composition and the upper protecting material of the solar cell or the solar cell element.

As the silane coupling agent in the present invention, there is included, for example, γ-chloropropyltrimethoxysilane; vinyltrichlorosilane; vinyltriethoxysilane; vinyltrimethoxysilane; vinyl-tris-(β-methoxyethoxy)silane; γ-methacryloxypropyltrimethoxysilane; β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane; γ-glycidoxypropyltrimethoxysilane; vinyltriacetoxysilane; γ-mercaptopropyltrimethoxysilane; γ-aminopropyltrimethoxysilane; N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane or the like. It is preferably vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and 3-acryloxypropyltrimethoxysilane.

These silane coupling agents are used in an amount of 0 to 5 parts by weight, preferably 0.01 to 5 parts by weight, more preferably 0.01 to 2 parts by weight, still more preferably 0.1 to 2 parts by weight, particularly preferably 0.5 to 1 part by weight, and most preferably 0.05 to 1 part by weight, relative to 100 parts by weight of the ethylene•α-olefin copolymer.

(5) The Hindered Amine-type Light Stabilizer (D)

In the present invention, it is preferable to blend the hindered amine-type light stabilizer to the resin composition. The hindered amine-type light stabilizer is used to capture radical species hazardous to a polymer and inhibit generation of new radicals. As the hindered amine-type light stabilizer, there are many kinds of compounds from a low molecular weight-type to a high molecular weight-type, and it may be used without any special limitation, as long as it is a conventionally known one.

As the low molecular weight-type hindered amine-type light stabilizer, there is included the one composed of 70% by weight of a reaction product of bis(2,2,6,6-tetramethyl-1-(octyloxy)-4-piperidinyl) ecanedioate (molecular weight: 737), 1,1-dimethyethyl hydroperoxide, and octane and 30% by weight of polypropylene; bis(1,2,2,6,6-pentamethyl-4-piperidyl) [[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]butyl malonate (molecular weight: 685); a mixture of bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate and methyl 1,2,2,6,6-pentamethyl-4-piperidyl sebacate(molecular weight: 509); bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate (molecular weight: 481); tetrakis(2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butane tetracarboxylate (molecular weight: 791); tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)-1,2,3,4-butane tetracarboxylate (molecular weight: 847); a mixture of 2,2,6,6-tetramethyl-4-piperidyl-1,2,3,4-butanetetracarboxylate and tridecyl-1,2,3,4-butane tetracarboxylate (molecular weight: 900); a mixture of 1,2,2,6,6-pentamethyl-4-piperidyl-1,2,3,4-butane tetracarboxylate and tridecyl-1,2,3,4-butane tetracarboxylate (molecular weight: 900) or the like.

As the high molecular weight-type hindered amine-type light stabilizer, there is included poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}] (molecular weight: 2,000-3,100); a polymerization product of dimethyl succinate and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol (molecular weight: 3100-4000); a mixture of N,N′,N″,N″′-tetrakis-(4,6-bis-(butyl-(N-methyl-2,2,6,6-tetramethylpiperidine-4-yl)amino)-triazine-2-yl)-4,7-diazadecane-1,10-diamine (molecular weight: 2286) and the above-described polymerization product between dimethyl succinate and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol; a polycondensate (molecular weight: 2600-3400) of dibutylamine-1,3,5-triazine-N,N′-bis(2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethylene diamine and N-(2,2,6,6-tetramethyl-4-piperidyl)butylamine, and a copolymer of a cyclic aminovinyl compound such as 4-acryloyloxy-2,2,6,6-tetramethylpiperidine, 4-acryloyloxy-1,2,2,6,6-pentamethylpiperidine, 4-acryloyloxy-1-ethyl-2,2,6,6-tetramethylpiperidine, 4-acryloyloxy-1-propyl-2,2,6,6-tetramethylpiperidine, 4-acryloyloxy-1-butyl-2,2,6,6-tetramethylpiperidine, 4-methacryloyoxy-2,2,6,6-tetramethylpiperidine, 4-methacryloyoxy-1,2,2,6,6-pentamethylpiperidine, 4-methacryloyoxy-1-ethyl-2,2,6,6-tetramethylpiperidine, 4-methacryloyoxy-1-butyl-2,2,6,6-tetramethylpiperidine, 4-crotonoyloxy-2,2,6,6-tetramethylpiperidine, 4-crotonoyloxy-1-propyl-2,2,6,6-tetramethylpiperidine, and ethylene; and the like. The above hindered amine-type light stabilizers may be used alone or by mixing two or more kinds.

Among these, as the hindered amine-type light stabilizer, it is preferable to use poly[{6-(1,1,3,3-tetramethylbutyl)amino-1,3,5-triazine-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}] (molecular weight: 2,000-3,100); a polymerization product (molecular weight: 3100-4000) of dimethyl succinate and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol; a mixture of N,N′,N″,N″′-tetrakis-(4,6-bis(butyl-(N-methyl-2,2,6,6-tetramethylpiperidine-4-yl)amino)-triazine-2-yl)-4,7-diazadecane-1,10-diamine (molecular weight: 2286) and the above polymerization product of dimethyl succinate and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol; a polycondensate (molecular weight: 2,600-3,400) of dibutylamine-1,3,5-triazine-N,N′-bis(2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethylene diamine and N-(2,2,6,6-tetramethyl-4-piperidyl)butylamine; a copolymer of a cyclic aminovinyl compound and ethylene•It is because bleeding out with time of the hindered amine-type light stabilizer can be prevented in use of a product. In addition, it is preferable to use the hindered amine-type light stabilizer having a melting point of 60° C. or higher, in view of easiness in preparing the composition.

In the present invention, content of the hindered amine-type light stabilizer is set at 0.01 to 2.5 parts by weight, preferably 0.01 to 1.0 part by weight, more preferably 0.01 to 0.5 part by weight, still more preferably 0.01 to 0.2 part by weight, and most preferably 0.03 to 0.1 part by weight, relative to 100 parts by weight of the above ethylene•α-olefin copolymer.

By setting the above content at 0.01 parts by weight or more, sufficient stabilization effect can be obtained, while by setting it at 2.5 parts by weight or less, discoloration of a resin caused by excess addition of the hindered amine-type light stabilizer can be suppressed.

In addition, weight ratio (B:D) of the above organic peroxide (B) and the above hindered amine light stabilizer (D) is set 1:0.1 to 1:10, and preferably 1:0.2 to 1:6.5. In this way, yellowing of a resin can be suppressed significantly.

(6) A Cross-linking Auxiliary Agent

In addition, the cross-linking auxiliary agent may be blended into the resin composition of the present invention.

The cross-linking auxiliary agent promotes a cross-linking reaction and is effective to enhance cross-linking degree of the ethylene•α-olefin copolymer, and as a specific example thereof, a poly-unsaturated compound such as a polyallyl compound and a poly(meth)acryloyloxy compound may be exemplified.

More specifically, there may be included a polyallyl compound such as triallyl isocyanurate, triallyl cyanurate, diallyl phthalate, diallyl fumarate, or diallyl maleate; a poly(meth)acryloxy compound such as ethylene glycol diacrylate, ethylene glycol dimethacrylate, or trimethylolpropane trimethacrylate; and divinylbenzene; or the like. The cross-linking auxiliary agent may be blended in a ratio of about 0 to 5 parts by weight, relative to 100 parts by weight of the component (A).

(7) An Ultraviolet Absorbing Agent

The ultraviolet absorbing agent may be blended into the resin composition of the present invention. As the ultraviolet absorbing agent, various types such as benzophenone-type, benzotriazole-type, triazine-type, and salicylate ester-type may be included.

The benzophenone-type ultraviolet absorbing agent may include, for example, 2-hydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-2′-carboxybenzophenone, 2-hydroxy-4-n-octoxybenzophenone, 2-hydroxy-4-n-dodecyloxybenzophenone, 2-hydroxy-4-n-octadecyloxybenzophenone, 2-hydroxy-4-benzyloxybenzophenone, 2-hydroxy-4-methoxy-5-sulfobenzophenone, 2-hydroxy-5-chlorobenzophenone, 2,4-dihydroxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, 2,2′-dihydroxy-4,4′-dimethoxybenzophenone, or 2,2′,4,4′-tetrahydroxybenzophenone, or the like.

The benzotriazole-type ultraviolet absorbing agent is a hydroxyphenyl substituted benzotriazole compound, may include, for example, 2-(2-hydroxy-5-methylphenyl)benzotriazole, 2-(2-hydroxy-5-t-butylphenyl)benzotriazole, 2-(2-hydroxy-3,5-dimethyphenyl)benzotriazole, 2-(2-methyl-4-hydroxyphenyl)benzotriazole, 2-(2-hydroxy-3-methyl-5-t-butylphenyl)benzotriazole, 2-(2-hydroxy-3,5-di-t-amylphenyl)benzotriazole, 2-(2-hydroxy-3,5-di-t-butylphenyl)benzotriazole or the like. In addition, the triazine type ultraviolet absorber includes, 2-[4,6-bis(2,4-dimethyphenyl)-1,3,5-triazine-2-yl]-5-(octyl oxy)phenol, 2-(4,6-diphenyl-1,3,5-triazine-2-yl)-5-(hexyloxy)phenol or the like. The salicylic acid ester type includes phenyl salicylate, p-octylphenyl salicylate or the like.

These ultraviolet absorbing agents is blended in an amount of 0 to 2.0 parts by weight, preferably 0.05 to 2.0 parts by weight, more preferably 0.1 to 1.0 part by weight, still more preferably 0.1 to 0.5 part by weight, and most preferably 0.2 to 0.4 part by weight, relative to 100 parts by weight of the ethylene•α-olefin copolymer.

(8) Other Additive Components

Other additive arbitrary components may be blended in the resin composition of the present invention within a range not to impair objectives of the present invention. Such an arbitrary additive component includes an antioxidant, a crystallization nucleating agent, a transparency enhancing agent, a lubricant, a coloring agent, a dispersing agent, a filler, a fluorescent whitening agent, a ultraviolet absorbing agent, a light stabilizer, which are used in a usual polyolefin-type resin material, or the like.

In addition, a rubber-type compound such as a crystalline ethylene•α-olefin copolymer obtained by polymerization using a Ziegler-type or a metallocene-type catalyst; and/or ethylene•α-olefin elastomer such as EBR or EPR; or styrene-type elastomer such as SEBS, a hydrogenated styrene block copolymer or the like may also be blended in 3 to 75 parts by weight into the resin composition of the present invention to provide flexibility or the like, within a range not to impair objectives of the present invention. Still more, in order to provide melt tension or the like, low density polyethylene produced by a high pressure method may be blended in 3 to 75 parts by weight as well.

2. The Solar Cell Encapsulant

The solar cell encapsulant (hereinafter may be referred to simply as a encapsulant) of the present invention is the one prepared by pelletizing or sheeting the above resin composition.

By using this solar cell encapsulant, the solar cell module can be produced by fixing the solar cell element together with the upper and lower protecting materials. As such a solar cell module, various types may be exemplified. For example, there may be exemplified the one having a composition where the solar cell element is sandwiched from both sides thereof with the encapsulant, such as the upper transparent protecting material/the encapsulant/the solar cell element/the encapsulant/the lower protecting material; the one having a composition where the encapsulant and the upper transparent protecting material are formed on the solar cell element formed on the inner circumference plane of the lower substrate protecting material; the one having a composition where the encapsulant and the lower protecting material are formed on the solar cell element formed on the inner circumference plane of the upper transparent protecting material, for example, the one where an amorphous solar cell element is prepared by sputtering or the like on a fluorocarbon resin-type transparent protecting material; or the like.

The solar cell element is not especially limited, and various types of solar cell elements may be used, such as a silicon-type such as monocrystalline silicon, polycrystalline silicon, or amorphous silicon; a III-V group and II-VI group compound semiconductor system of such as gallium-arsenic, copper-indium-selenium, cadmium-tellurium.

As the upper protecting material composing the solar cell module, glass, an acrylic resin, polycarbonate, polyester, a fluorine-containing resin or the like may be exemplified.

In addition, the lower protecting material is a simple substance or multi-layer sheet of a metal or various thermoplastic resin films, for example, a single layer or multi-layer protecting film of such as a metal including tin, aluminum, stainless steel; an inorganic material such as glass; polyester, polyester vapor deposited with an inorganic substance; a fluorine-containing resin; a polyolefin or the like may be exemplified. To such an upper and/or lower protecting material, primer treatment may be performed to enhance adhesion property with the encapsulant. In the present invention, as the upper protecting material, glass and the fluorine-containing resin are preferable.

The solar cell encapsulant of the present invention may be used as pellets, however, it may be used by molding to a sheet-shape with a thickness of usually about 0.1 to 1 mm. The thickness less than 0.1 mm provides weak strength and insufficient adhesion, while the thickness more than 1 mm may raise a problem caused by decreased transparency. Preferable thickness is 0.1 to 0.8 mm.

The sheet-shape solar cell encapsulant can be produced by a known sheet molding method using a T-die extruder, a calender machine or the like. For example, it may be obtained by adding a cross-linking agent to the ethylene•α-olefin copolymer, dry blending in advance, if necessary, a hindered amine-type light stabilizer, and still more a cross-linking auxiliary agent, a silane coupling agent, a ultraviolet absorbing agent, an antioxidant, a light stabilizer or the like, to supply from a hopper of the T-die extruder, and performing extrusion molding to the sheet-shape at an extrusion temperature of 80 to 150° C. In such dry-blending, a part of or the whole additives may be used as a master batch form. In addition, in T-die extrusion or calender molding, a resin composition may also be used which is obtained by melt mixing a part of or the whole additives, in advance, to the ethylene•α-olefin copolymer, using a single screw extruder, a twin screw extruder, a Banbury mixer, a kneader or the like.

In producing the solar cell module, a module having the aforesaid composition may be formed by a method for preparing a sheet of the encapsulant of the present invention, in advance, and press-adhering it at temperature for melting the resin composition of the encapsulant, for example, 150 to 200° C. In addition, by adopting a method for laminating the solar cell element or the upper protecting material or the lower protecting material, by extrusion coating of the encapsulant of the present invention, the solar cell module can be produced in one stage without sheet molding separately. Use of the encapsulant of the present invention, consequently, is capable of improving productivity of the module significantly.

On the other hand, in producing the solar cell module, by adhering tentatively the solar cell element or said encapsulant to the protecting material at such temperature that the organic peroxide does not substantially decompose and the encapsulant of the present invention melts, and then by raising temperature, sufficient adhesion and cross-linking of the ethylene•α-olefin copolymer may be performed. In this case, in order to obtain the solar cell module having good heat resistance such as a melting point (a DSC method) of the encapsulant layer of 40° C. or higher and a storage elastic modulus at 150° C. of 10³ Pa or higher, it is preferable to perform cross-linking so as to obtain a gel fraction (obtained by immersing 1 g of a sample into 100 ml of xylene, heating at 110° C. for 24 hours, and then measuring mass fraction of a unmelted portion by filtering with a 20 mesh metal screen) in the encapsulant layer of 50 to 98%, and preferably about 70 to 95%.

It should be noted that, in the PATENT LITERATURE 3, a sheet with a thickness of 0.5 mm was produced at a processing temperature of 100° C., using a profile extruder, from a mixture obtained by mixing 1.5 part by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, as the organic peroxide, and 2 parts by weight of triallyl isocyanurate, as the cross-linking auxiliary agent (Example 3). However, selection of such a composition cannot provide sufficient productivity due to low processing temperature.

In an encapsulation work of the solar cell element, there is a method for covering the solar cell element with the above encapsulant of the present invention, then adhering tentatively it by heating at such temperature that the organic peroxide does not decompose for about several minutes to ten minutes, and then adhering it by heat treating in an oven at high temperature of about 150 to 200° C., at which the organic peroxide decomposes, for 5 minutes to 30 minutes or the like.

It should be noted that the resin composition of the present invention is optimal as the encapsulant of the solar cell module, as described above, however, it may also be applied preferably, other than this, in producing water shielding sheet, or Tarpaulin, or encapsulating of an IC (integrated circuit).

EXAMPLES

Explanation will be given below specifically on the present invention with reference to Examples, however, the present invention should not be limited to these Examples. It should be noted that evaluation methods and resins used in Examples and Comparative Examples are as follows.

1. Evaluation Methods for Resin Properties

-   (1) Melt flow rate (MFR): MFR of the ethylene•α-olefin copolymer was     measured in accordance with JIS-K6922-2: 1997 attachment (at 190°     C., under a load of 21.18 N). -   (2) Density: Density of the ethylene•α-olefin copolymer was measured     in accordance with JIS-K6922-2: 1997 attachment (at 23° C., the case     of a low density polyethylene), as described above. -   (3) Mz/Mn: It was measured by GPC, as described above. -   (4) Melt viscosity:

Melt viscosity (η*₁) under a shear rate of 2.43×10 sec⁻¹, and melt viscosity (η*₂) under a shear rate of 2.43×10² sec⁻¹ were measured using Capillograph 1-B, manufactured by Toyo Seiki Seisaku-sho Ltd., and using a capillary with D=1 mm, L/D=10, at a set temperature of 100° C., in accordance with JIS-K7199-1999.

-   (5) Branch number:

Branch number (N) in a polymer was measured by NMR under the following conditions, and comonomer amount was determined as number per total 1000 carbons of a main chain and a side chain.

-   Apparatus: AVANCE III cryo-400 MHz, manufactured by Bruker     BioSpin K. K. -   Solvent: Ortho-dichlorobenzene/deuterated bromobenzene=8/2 mixed     solution     <Amount of a Sample> -   460 mg/2.3 ml     <C-NMR>     -   H-decoupling and NOE present     -   Cumulative number: 256 scans     -   Flip angle: 90 degree     -   Pulse interval: 20 seconds     -   AQ (incorporation time): 5.45 s, D1 (waiting time)=14.55 s -   (6) FR: Ratio (I₁₀/I_(2.16)) of an MFR measured value (I₁₀) at     190° C. under a load of 10 kg, and an MFR measured value (I_(2.16))     at 190° C. under a load of 2.16 kg was calculated, in accordance     with JIS-K7210-1999, to be used as FR.     2. Evaluation Methods for an Extrusion Molding (Sheet)     (1) Haze

It was measured using a pressed sheet with a thickness of 0.7 mm, in accordance with JIS-K7136-2000. The pressed sheet was set in a glass cell filled with special grade liquid paraffin, produced by Kanto Chemical Co., Inc., to measure Haze. The pressed sheet was prepared by storing it in a hot press machine under a temperature condition of 160° C. for 30 minutes for cross-linking. The smaller haze value shows the better performance.

(2) Light Transmittance

It was measured using a pressed sheet with a thickness of 0.7 mm, in accordance with JIS-K7136-1997. The pressed sheet was set in a glass cell filled with special grade liquid paraffin, produced by Kanto Chemical Co., Inc., to measure light transmittance. The pressed sheet was prepared by storing it in a hot press machine under a temperature condition of 160° C. for 30 minutes for cross-linking.

Light transmittance is 80% or more, preferably 85% or more, and still preferably 90% or more.

(3) Tensile Modulus

Tensile Modulus was measured using a pressed sheet with a thickness of 0.7 mm, in accordance with ISO1184-1983. It should be noted that Tensile Modulus was determined at a elongation rate of 1%, under conditions of an elongation speed of 1 mm/min, a test piece width of 10 mm, and a distance between grippers of 100 mm. The smaller value shows the more superior flexibility.

(4) Heat Resistance

It was evaluated by gel fraction of a sheet cross-linked at 160° C. for 30 minutes, and a sheet cross-linked at 150° C. for 30 minutes. The higher gel fraction shows more progress of cross-linking and is evaluated as having higher heat resistance. The one with the gel fraction of 70% by weight was ranked “∘” in evaluation of heat resistance. It should be noted that the gel fraction is calculated by accurately weighing about 1 g of the relevant sheet, immersing it in 100 cc of xylene, treating it at 110° C. for 24 hours, drying the residue after filtration, accurately weighing, and dividing it with weight before the treatment.

(5) Adhesion Property with Glass

A slide glass with a size of 7.6 cm×2.6 cm and a thickness of 1 mm was used. A resin composition was contacted with the slide glass, and performed heating under a condition of 160° C. for 30 minutes, using a press machine. Evaluation was performed after standing it in atmosphere of 23° C. for 24 hours, and ranked [x] when the resin was peeled from the slide glass by hands, and [∘] when it was not peeled.

3. Raw Materials Used

-   (1) The component (A): the ethylene•α-olefin Copolymer

A copolymer of ethylene and 1-hexene polymerized in the following <Production Example 1> (PE-1), a copolymer of ethylene and 1-butene polymerized in the following <Production Example 2> (PE-2), and commercially available ethylene•α-olefin copolymers (PE-3), (PE-6) and (PE-7), and copolymers of ethylene and 1-hexene polymerized in the following <Production Example 3 and 4> (PE-4), (PE-5) were used. The properties are shown in Table 1.

-   (2) The silane coupling agent: γ-methacryloxypropyltrimethoxysilane     (KBM503, produced by Shin-Etsu Chemical Co., Ltd.) -   (3) The organic peroxide: 2,5-dimethyl-2,5-di(t-butylperoxy)hexane     (Luperox 101, produced by Arkema-Yoshitomi Co. Ltd.) -   (4) The hindered amine-type light stabilizer (a): a polycondensate     of     dibutylamine-1,3,5-triazine-N,N′-bis(2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethylene     diamine and N-(2,2,6,6-tetramethyl-4-piperidyl)butylamine     (CHIMASSORB 2020FDL, produced by Ciba-Japan K.K.) -   (5) The hindered amine-type light stabilizer (b): a polymerization     product of dimethyl succinate and     4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol (TINUVIN 622LD,     produced by Ciba-Japan K.K.) -   (6) The ultraviolet absorbing agent:     2-hydroxy-4-n-octoxybenzophenone (CYTEC UV531, produced by Sun     Chemical Co. Ltd.)

Production Example 1

(i) Preparation of a Catalyst

A catalyst for producing a copolymer of ethylene and 1-hexene was prepared by a method described in JP-A-7-508545. That is, into 2.0 mmol of a complex of dimethylsilylenebis(4,5,6,7-tetrahydroindenyl)hafnium dimethyl, equimolar amount of tripentafluorophenylboron, based on the above complex, was added, and by dilution with toluene to 10 L, a catalyst solution was prepared.

(ii) Polymerization

Using a stirring-type autoclave-type continuous reactor with an inner volume of 1.5 L, a mixture of ethylene and 1-hexene, as a raw material gas, was continuously supplied in a rate of 40 kg/hr, so that the composition of 1-hexene was 75% by weight, under maintaining pressure inside the reactor at 130 MPa. In addition, the above catalyst solution was supplied continuously by adjusting supply amount thereof so as to maintain polymerization temperature at 150° C. Production amount of the polymer was about 4.3 kg per hour. After completion of the reaction, the ethylene•1-hexene copolymer (PE-1), with a content of 1-hexene of 24% by weight, an MFR of 35 g/10 min, a density of 0.880 g/cm³, and a Mz/Mn of 3.7, was obtained.

In addition, after preheating the PE-1 under a condition of 160° C-0 kg/cm² for 3 minutes, it was pressurized under a condition of 160° C-100 kg/cm² for 5 minutes, and then by cooling it with a cooling press set at 30° C., under a condition of 100 kg/cm² for 10 minutes, a pressed sheet with a thickness of 0.7 mm was obtained. As a result of performing measurement of Tensile Modulus thereof, in accordance with IS01184-1983, it was 17 MPa.

Characteristics of this ethylene•1-hexene copolymer (PE-1) is shown in Table 1.

Production Example 2

Polymerization was performed by changing monomer composition and polymerization temperature in polymerization in Production Example 1, so as to attain composition, density and melt viscosity shown in Table 1. After completion of the reaction, the ethylene•1-butene copolymer (PE-2), with content of 1-butene=35% by weight, MFR=33 g/10 min, density=0.870 g/cm³, and Mz/Mn=3.5, was obtained. As a result of performing measurement of Tensile Modulus thereof, similarly as in Production Example 1, it was found to be 8 MPa. Characteristics of this ethylene•1-butene copolymer (PE-2) is shown in Table 1.

Production Example 3

Polymerization was performed by a similar method as in Production Example 1, except that composition of 1-hexene in polymerization was changed to 74% by weight and polymerization temperature was changed to 135° C. in Production Example 1. Production amount of the polymer was about 3.3 kg per hour. After completion of the reaction, the ethylene•1-hexene copolymer (PE-3), with content of 1-hexene=24% by weight, MFR=8 g/10 min, density=0.880 g/cm³, and Mz/Mn=3.7, was obtained. As a result of performing measurement of Tensile Modulus thereof, similarly as in Production Example 1, it was found to be 17 MPa. Characteristics of this ethylene•1-hexene copolymer (PE-3) is shown in Table 1.

Production Example 4

Polymerization was performed by a similar method as in Production Example 1, except that composition of 1-hexene in polymerization was changed to 71% by weight and polymerization temperature was changed to 157° C. in Production Example 1. Production amount of the polymer was about 4.0 kg per hour. After completion of the reaction, the ethylene•1-hexene copolymer (PE-4), with content of 1-hexene=19% by weight, MFR=30 g/10 min, density=0.890 g/cm³, and Mz/Mn=3.7, was obtained. As a result of performing measurement of Tensile Modulus thereof, similarly as in Production Example 1, it was found to be 34 MPa. Characteristics of this ethylene•1-hexene copolymer (PE-4) is shown in Table 1.

TABLE 1 Branch Number Content of α- Mz/ piece/ Tensile Polymerization olefin (Note) Density Mn total Modulus η*₁ η*₂ η*₁/ catalyst wt % g/cm³ — 1000C Mpa poise poise η*₂ FR PE-1 Production Example 1 Metallocene 24 (C6) 0.880 3.7 44 17 2.3 × 10⁴ 1.2 × 10⁴ 1.9 5.9 PE-2 Production Example 2 Metallocene 35 (C4) 0.870 3.5 67  8 2.2 × 10⁴ 1.2 × 10⁴ 1.8 5.9 PE-3 TufmerA4085S — 19 (C4) 0.885 3.5 53 27 9.2 × 10⁴ 1.9 × 10⁴ 4.8 5.9 PE-4 Production Example 3 Metallocene 24 (C6) 0.880 3.7 44 17 6.9 × 10⁴ 1.7 × 10⁴ 4.1 5.9 PE-5 Production Example 4 Metallocene 19 (C6) 0.890 3.7 35 34 2.5 × 10⁴ 1.2 × 10⁴ 2.1 5.9 PE-6 ENGAGE 8200 — 36 (C8) 0.870 3.6 45  8 7.8 × 10⁴ 2.0 × 10⁴ 3.9 7.5 PE-7 ENGAGE 8400 — 36 (C8) 0.870 3.2 45  8 2.6 × 10⁴ 1.0 × 10⁴ 2.6 7.5 (Note): (C4), (C6) and (C8) are carbon numbers of an α-olefin used as a comonomer.

Example 1

1.5 parts by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (Luperox 101, produced by Arkema-Yoshitomi Co. Ltd.) as an organic peroxide and 0.2 part by weight of a polycondensate of dibutylamine-1,3,5-triazine-N,N′-bis(2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethlene diamine and N-(2,2,6,6-tetramethyl-4-piperidyl)butylamine (CHIMASSORB, produced 2020FDL by Chiba-Japan K.K.), as a hindered amine-type light stabilizer (a), were blended relative to 100 parts by weight of the copolymer of ethylene and 1-hexene (PE-1). They were sufficiently mixed and pelletized using a 40 mmφ single-screw extruder, under conditions of a set temperature of 130° C. and extrusion rate of 17 kg/hr.

After preheating the resultant pellets under a condition of 160° C-0 kg/cm² for 3 minutes, they were pressurized under a condition of 160° C-100 kg/cm² for 27 minutes (press molding at 160° C. for 30 minutes), and then by cooling them with a cooling press set at 30° C., under a condition of 100 kg/cm² for 10 minutes, a pressed sheet with a thickness of 0.7 mm was obtained. Haze, light transmittance, Tensile Modulus and heat resistance of the sheet were measured and evaluated. Evaluation results are shown in Table 2.

Example 2

A sheet was produced similarly as in Example 1, except that PE-2 was used instead of PE-1, in Example 1. Haze, light transmittance, Tensile Modulus and heat resistance of the sheet were measured and evaluated. Evaluation results are shown in Table 2.

Example 3

A sheet was produced similarly as in Example 1, except that a polymerization product of dimethyl succinate and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol was used as the hindered amine-type light stabilizer (b), in Example 1. Haze, light transmittance, Tensile Modulus and heat resistance of the sheet were measured and evaluated. Evaluation results are shown in Table 2.

Example 4

A sheet was produced similarly as in Example 3, except that PE-2 was used instead of PE-1, in Example 3. Haze, light transmittance, Tensile Modulus and heat resistance of the sheet were measured and evaluated. Evaluation results are shown in Table 2.

Example 5

A sheet was produced similarly as in Example3, except that PE-4 was used instead of PE-1, in Example 3. Haze, light transmittance, Tensile Modulus and heat resistance of the sheet were measured and evaluated. Evaluation results are shown in Table 2.

Example 6

A sheet was produced similarly as in Example3, except that PE-5 was used instead of PE-1, in Example 3. Haze, light transmittance, Tensile Modulus and heat resistance of the sheet were measured and evaluated. Evaluation results are shown in Table 2.

Example 7

A sheet was produced similarly as in Example 1, except that 0.3 part of 2-hydroxy-4-n-octoxybenzophenone (CYTEC UV531, produced by Sun Chemical Co. Ltd.) was further added, as the ultraviolet absorbing agent, in Example 3. Haze, light transmittance, Tensile Modulus and heat resistance of the sheet were measured and evaluated. Evaluation results are shown in Table 2.

Example 8

A sheet was produced similarly as in Example 1, except that 0.3 part of 2-hydroxy-4-n-octoxybenzophenone (CYTEC UV531, produced by Sun Chemical Co. Ltd.) was further added, as the ultraviolet absorbing agent, in Example 4. Haze, light transmittance, Tensile Modulus and heat resistance of the sheet were measured and evaluated. Evaluation results are shown in Table 2.

Comparative Example 1

Pelletization was tried similarly as in Example 1, except that PE-3 (TufmerA4085S, an ethylene•1-butene copolymer, produced by Mitsui Chemical, Inc.) was used instead of the copolymer of ethylene and 1-hexene (PE-1). However, increase in resin temperature caused by shear heat generation accelerated decomposition rate of the organic peroxide, progressed cross-linking and thus did not provide pellets.

Comparative Example 2

Pelletization was performed by changing extruder conditions so that set temperature was 100° C. and extrusion rate was 9.7 kg/hr in Comparative Example 1, and still more performed sheeting to evaluate the resultant sheet. Results are shown in Table 2. High extrusion rate was not attainable, resulting in inferior productivity.

Comparative Example 3

Pelletization was tried similarly as in Example 1, except that PE-6 (ENGAGE8200, an ethylene•1-octene copolymer, produced by Dow Chemical Co., Ltd.) was used instead of PE-1. However, increase in resin temperature caused by shear heat generation accelerated decomposition rate of the organic peroxide, progressed cross-linking and thus did not provide pellets.

Comparative Example 4

A sheet was produced similarly as in Example 1, except that PE-7 (ENGAGE8400, an ethylene•1-octene copolymer, produced by Dow Chemical, Co., Ltd.) was used instead of PE-1. Haze, light transmittance, Tensile Modulus and heat resistance of the sheet were measured and evaluated. Evaluation results are shown in Table 2. Cross-linking efficiency was poor, resulting in inferior heat resistance.

TABLE 2 Com- Com- Com- Com- ara- ara- ara- ara- Ex- Ex- Ex- Ex- Ex- Ex- Ex- Ex- tive tive tive tive am- am- am- am- am- am- am- am- Exam- Exam- Exam- Exam- ple 1 ple 2 ple 3 ple 4 ple 5 ple 6 ple 7 ple 8 ple 1 ple 2 ple 3 ple 4 Ethylene · α-olefin PE-1 Parts 100 — 100 — — — 100 — — — — — copolymer PE-2 by — 100 — 100 — — — 100 — — — — PE-3 weight — — — — — — — — 100 100 — — PE-4 — — — — 100 — — — — — — — PE-5 — — — — — 100 — — — — — — PE-6 — — — — — — — — — — 100 — PE-7 — — — — — — — — — — — 100 Satisfaction of formula (a) ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ X X Organic peroxide 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Hindered amine (a) 0.2 0.2 — — — — — — 0.2 0.2 0.2 0.2 Hindered amine (b) — — 0.05 0.05 0.05 0.05 0.05 0.05 — — — — Ultraviolet absorbing agent — — — — — — 0.3 0.3 — — — — Extrusion temperature ° C. 130 130 130 130 130 130 130 130 130 100 130 130 Extrusion rate kg/hr 17 17 17 17 17 17 17 17 No pellet 9.7 No pellet 17 Haze % 4.4 2.5 4.4 2.5 4.4 4.0 4.5 2.6 — 5.0 — 4.2 Light transmittance % 91 91 91 91 91 91 91 91 — 91 — 91 Modulus of elasticity Mpa 18 9 18 9 18 35 18 9 — 28 — 9 in tension Heat resistance — ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ — ◯ — ◯ (160° C. × 30 min) Heat resistance — ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ — ◯ — X (150° C. × 30 min)

Example 9

1.5 part by weight of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (Luperox 101, produced by Arkema-Yoshitomi Co. Ltd.), as an organic peroxide, and 0.2 part by weight of a polycondensate of dibutylamine-1,3,5-triazine-N,N′-bis(2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethlene diamine and N-(2,2,6,6-tetramethyl-4-piperidyl)butylamine (CHIMASSORB, produced 2020FDL by Chiba-Japan K.K.), as a hindered amine-type light stabilizer (a), were blended relative to 100 parts by weight of the copolymer of ethylene and 1-hexene (PE-1). They were sufficiently mixed and pelletized using a 40 mmφ single-screw extruder, under conditions of a set temperature of 130° C. and extrusion rate of 17 kg/hr.

After preheating the resultant pellets under a condition of 160° C-0 kg/cm² for 3 minutes, they were pressurized under a condition of 160° C-100 kg/cm² for 27 minutes (press molding at 160° C. for 30 minutes), and then by cooling them with a cooling press set at 30° C., under a condition of 100 kg/cm² for 10 minutes, a pressed sheet with a thickness of 0.7 mm was obtained. Haze, light transmittance, Tensile Modulus, heat resistance and adhesion property of the sheet were measured and evaluated. Evaluation results are shown in Table 3.

Example 10

A sheet was produced similarly as in Example 9, except that PE-2 was used instead of PE-1, in Example 9. Haze, light transmittance, Tensile Modulus, heat resistance and adhesion property of the sheet were measured and evaluated. Evaluation results are shown in Table 3.

Example 11

A sheet was produced similarly as in Example 9, except that 0.05 part of a polymerization product of dimethyl succinate and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidine ethanol was used, as the ultraviolet absorbing agent (b), in Example 9. Haze, light transmittance, Tensile Modulus, heat resistance and adhesion property of the sheet were measured and evaluated. Evaluation results are shown in Table 2.

Example 12

A sheet was produced similarly as in Example 11, except that PE-2 was used instead of PE-1, in Example 11. Haze, light transmittance, Tensile Modulus, heat resistance and adhesion property of the sheet were measured and evaluated. Evaluation results are shown in Table 3.

Example 13

A sheet was produced similarly as in Example 11, except that PE-4 was used instead of PE-1, in Example 11. Haze, light transmittance, Tensile Modulus, heat resistance and adhesion property of the sheet were measured and evaluated. Evaluation results are shown in Table 3.

Example 14

A sheet was produced similarly as in Example 11, except that PE-5 was used instead of PE-1, in Example 11. Haze, light transmittance, Tensile Modulus, heat resistance and adhesion property of the sheet were measured and evaluated. Evaluation results are shown in Table 3.

Example 15

A sheet was produced similarly as in Example 11, except that 0.3 part of 2-hydroxy-4-n-octoxybenzophenone (CYTEC UV531, produced by Sun Chemical Co. Ltd.) was further added, as the ultraviolet absorbing agent, in Example 11. Haze, light transmittance, Tensile Modulus, heat resistance and adhesion property of the sheet were measured and evaluated. Evaluation results are shown in Table 3.

Example 16

A sheet was produced similarly as in Example 12, except that 0.3 part of 2-hydroxy-4-n-octoxybenzophenone (CYTEC UV531, produced by Sun Chemical Co. Ltd.) was further added, as the ultraviolet absorbing agent, in Example 12. Haze, light transmittance, Tensile Modulus, heat resistance and adhesion property of the sheet were measured and evaluated. Evaluation results are shown in Table 3.

Comparative Example 5

Pelletization was tried similarly as in Example 9, except that PE-3 (TufmerA4085S, an ethylene•1-butene copolymer, produced by Mitsui Chemical, Inc.) was used instead of the copolymer of ethylene and 1-hexene (PE-1). However, increase in resin temperature caused by shear heat generation accelerated decomposition rate of the organic peroxide, progressed cross-linking and thus did not provide pellets.

Comparative Example 6

Pelletization was performed by changing extruder conditions so that set temperature was 100° C. and extrusion rate was 9.7 kg/hr in Comparative Example 5, and still more performed sheeting to evaluate the resultant sheet. Results are shown in Table 3. High extrusion rate was not attainable, resulting in inferior productivity.

Comparative Example 7

Pelletization was tried similarly as in Example 9, except that PE-6 (ENGAGE8200, an ethylene•1-octene copolymer, produced by Dow Chemical Co., Ltd.) was used instead of PE-1. However, increase in resin temperature caused by shear heat generation accelerated decomposition rate of the organic peroxide, progressed cross-linking and thus did not provide pellets.

Comparative Example 8

A sheet was produced similarly as in Example 9, except that PE-7 (ENGAGE8400, an ethylene•1-octene copolymer, produced by Dow Chemical, Co., Ltd.) was used instead of PE-1. Haze, light transmittance, Tensile Modulus and heat resistance of the sheet were measured and evaluated. Evaluation results are shown in Table 3. Cross-linking efficiency was poor, resulting in inferior heat resistance.

TABLE 3 Com- Com- Com- Com- ara- ara- ara- ara- Ex- Ex- Ex- Ex- Ex- Ex- Ex- Ex- tive tive tive tive am- am- am- am- am- am- am- am- Exam- Exam- Exam- Exam- ple 9 ple 10 ple 11 ple 12 ple 13 ple 14 ple 15 ple 16 ple 5 ple 6 ple 7 ple 8 Ethylene · α-olefin PE-1 Parts 100 — 100 — — — 100 — — — — — copolymer PE-2 by — 100 — 100 — — — 100 — — — — PE-3 weight — — — — — — — — 100 100 — — PE-4 — — — — 100 — — — — — — — PE-5 — — — — — 100 — — — — — — PE-6 — — — — — — — — — — 100 — PE-7 — — — — — — — — — — — 100 Satisfaction of formula (a) ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ X X Organic peroxide 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Hindered amine (a) 0.2 0.2 — — — — — — 0.2 0.2 0.2 0.2 Hindered amine (b) — — 0.05 0.05 0.05 0.05 0.05 0.05 — — — — Silane coupling agent 1 1 1 1 1 1 1 1 1 1 1 1 UV absorbing agent — — — — — — 0.3 0.3 — — — — Extrusion temperature ° C. 130 130 130 130 130 130 130 130 130 100 130 130 Extrusion rate kg/hr 17 17 17 17 17 17 17 17 No pellet 9.7 No pellet 17 Haze % 4.4 2.5 4.4 2.5 4.4 4.0 4.5 2.6 — 5.0 — 4.2 Light transmittance % 91 91 91 91 91 91 91 91 — 91 — 91 Modulus of elasticity Mpa 20 10 20 10 20 34 18 9 — 23 — 10 in tension Heat resistance — ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ — ◯ — ◯ (160° C. × 30 min) Heat resistance — ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ — ◯ — X (150° C. × 30 min) Adhesion property — ◯ ◯ ◯ ◯ ◯ ◯ ◯ ◯ — ◯ — ◯ (to glass) [Evaluation]

As a result, as is clear from Tables 2 and 3, in Examples 1 to 16, because the resin composition of the present invention is used, the resultant sheet obtained by extrusion molding of this has small haze, large light transmittance, good balance among heat resistance, rigidity and cross-linking efficiency, and in particular, in Examples 9 to 16, also showed superior adhesion property to glass.

On the other hand, in Comparative Examples 1 and 5, because the resin composition containing ethylene•1-butene copolymer with melt viscosity outside and different from the present invention is used, pellets were not obtained. In Comparative Examples 2 and 6, sheets were molded due to decreased extrusion temperature, however, productivity was decreased significantly as compared with Examples 1 and 9. In addition, the resultant sheets had large haze and small flexibility, although showed superior heat resistance and adhesion property. In Comparative Examples 3 and 7, because the resin composition containing ethylene•1-octene copolymer with melt viscosity outside the present invention was used, pellets were not obtained. In Comparative Examples 4 and 8, because the resin composition containing ethylene•1-octene copolymer with the expression (a) and the FR outside the present invention was used, the resultant sheet showed poor cross-linking efficiency and inferior heat resistance.

Industrial Applicability

The resin composition for a solar cell encapsulant of the present invention is utilized as the solar cell encapsulant, where transparency, flexibility and balance between rigidity and cross-linking efficiency, weather resistance or the like is required. In particular, it is useful as the encapsulant of a thin film solar cell or a solar cell using a glass plate as a substrate. This resin composition may also be applied preferably, other than the solar cell encapsulant, in producing water shielding sheet, or Tarpaulin, or encapsulating of an IC (integrated circuit). 

The invention claimed is:
 1. A solar cell encapsulant, comprising a resin composition, which comprises: component (A), comprising an ethylene•α-olefin copolymer; and at least one selected from the group consisting of component (B) comprising an organic peroxide and component (C) comprising a silane coupling agent, wherein the ethylene•α-olefin copolymer has characteristics (a1) to (a4) and (a5) or (a6) (a1) a density of 0.860 to 0.920 g/cm³, (a2) a ratio, (Mz/Mn), of Z average molecular weight (Mz) and number average molecular weight (Mn) determined by a gel permeation chromatography (GPC), of 8.0 or less, (a3) a melt viscosity (η*₁) measured at 100° C. under a shear rate of 2.43×10 s⁻¹ of 9.0×10⁴ poise or less, (a4) a melt viscosity (η*₂) measured at 100° C. under a shear rate of 2.43×10² s⁻¹ of 1.8×10⁴ poise or less, and (a5) a branch number (N) derived from a comonomer in a polymer satisfying expression (a) N≧−0.67×E+53   (a), wherein N represents a branch number per total 1000 carbon atoms in a main chain and a side chain, measured by NMR, and E represents a Tensile Modulus of a sheet, measured in accordance with ISO1184-1983, or (a6) a flow ratio (FR): a ratio (I₁₀/I_(2.16)) of I₁₀ which is an MFR measured value at 190° C. under a load of 10 kg, and I_(2.16) which is an MFR measured value at 190° C. under a load of 2.16 kg, of below 7.0.
 2. The encapsulant of claim 1, wherein characteristic (a5) is present and satisfies expression (a′) −0.67×E+80≧N≧−0.67×E+53   (a′), wherein N represents the branch number per total 1000 carbon atoms in a main chain and a side chain, measured by NMR; and E represents the Tensile Modulus of a sheet, measured in accordance with ISO1184-1983.
 3. The encapsulant of claim 1, wherein characteristic (a6) is present and the flow ratio (FR) of (a6) is 5.0 to 6.2.
 4. The encapsulant of claim 1, wherein component (B) is present and a content of the component (B) is 0.2 to 5 parts by weight, relative to 100 parts by weight of the component (A).
 5. The encapsulant of claim 1, wherein component (C) is present and a content of the component (C) is 0.01 to 5 parts by weight, relative to 100 parts by weight of the component (A).
 6. The encapsulant of claim 1, wherein the resin composition further comprises: component (D) comprising a hindered amine light stabilizer.
 7. The encapsulant of claim 6, wherein a content of the component (D) is 0.01 to 2.5 parts by weight, relative to 100 parts by weight of the component (A).
 8. The encapsulant of claim 1, wherein the component (A) comprises an ethylene-1-butene copolymer.
 9. The encapsulant of claim 1, wherein the ethylene•α-olefin copolymer of the component (A) has a ratio (η*₁/η*₂) of melt viscosity (η*₁) and melt viscosity (η*₂), of 4.5 or less.
 10. The solar cell encapsulant of claim 1, obtained by pelletizing or sheeting the resin composition.
 11. A solar cell module, comprising the solar cell encapsulant of claim
 10. 12. The encapsulant of claim 1, wherein the component (A) comprises an ethylene•α-olefin copolymer.
 13. The encapsulant of claim 1, wherein a content of an α-olefin of the ethylene•α-olefin copolymer in the composition is 5 to 40% by weight.
 14. The encapsulant of claim 1, wherein a content of an α-olefin of the ethylene•α-olefin copolymer in the composition is 10 to 35% by weight.
 15. The encapsulant of claim 1, wherein a content of an α-olefin of the ethylene•α-olefin copolymer in the composition is 15 to 30% by weight.
 16. The encapsulant of claim 1, wherein the ethylene•α-olefin copolymer has a density (a1) of 0.870 to 0.915 g/cm³.
 17. The encapsulant of claim 1, wherein the ethylene•α-olefin copolymer has a density (a1) of 0.875 to 0.910 g/cm³.
 18. The encapsulant of claim 1, wherein the ratio, (Mz/Mn), is 5.0 or less.
 19. The encapsulant of claim 1, wherein the ratio, (Mz/Mn), is 4.0 or less.
 20. The encapsulant of claim 1, wherein the ratio, (Mz/Mn), is 2.0 or more. 